# Copyright (c) Meta Platforms, Inc. and affiliates import abc import io from collections.abc import Sequence from typing import cast, IO, Optional # introduced as collections.abc.Buffer in Python 3.12 from typing_extensions import Buffer from torch._utils import try_import # NOTE: everything in this file is experimental, and subject to # change. Feedback and bug fixes are always welcome. pyzstd_module_name = "pyzstd" pyzstd = try_import(pyzstd_module_name) zstandard_module_name = "zstandard" zstandard = try_import(zstandard_module_name) __all__ = [ "Extension", "StreamTransformExtension", "ZStandard", "ExtensionRegistry", ] class Extension(abc.ABC): """ Extensions provide modular additions to functionality within distributed checkpointing, which affect the layout or format of the written artifacts. Extensions may be built into pytorch, or provided externally. When writing, the caller provides a list of extension instances of the appropriate type. Each extension can output a descriptor which is used to reconstitute the extension at read-time. """ @staticmethod @abc.abstractmethod def registry_name() -> str: """ See ExtensionRegistry.from_descriptor_list """ @staticmethod @abc.abstractmethod def from_descriptor(version: str) -> "Extension": """ See ExtensionRegistry.from_descriptor_list """ @abc.abstractmethod def get_descriptor(self) -> str: """ Return descriptor name to be included in metadata. The form should be "extension_name[@local-domain][/version]". """ class StreamTransformExtension(Extension): """ An extension which performs transformation on a byte stream, such as compression or encryption. Implementations should try to be memory friendly and performant. For example, don't read the whole input, then transform it, and write it back. If at all possible, do it in chunks. But, don't read/transform/write one byte at a time, either. """ @abc.abstractmethod def transform_to(self, output: IO[bytes]) -> IO[bytes]: """ Takes a writeable output stream, and generates a new stream which implements the output transform. Input data written to the returned stream will be transformed and written to the `output` argument stream. """ @abc.abstractmethod def transform_from(self, input: IO[bytes]) -> IO[bytes]: """ Takes a readable input stream, and generates a new stream which implements the input transform. When the returned stream is read, data will be read from the 'input' stream, transformed, and returned. """ class ZStandard(StreamTransformExtension): @staticmethod def is_available() -> bool: return zstandard is not None or pyzstd is not None @staticmethod def from_descriptor(version: str) -> "ZStandard": if version.partition(".")[0] != "1": raise ValueError(f"Unknown extension {version=}") if not ZStandard.is_available(): raise ValueError( f"Stream with ZStandard compression cannot be processed because " f"no module named '{zstandard_module_name}' or '{pyzstd_module_name}'" ) return ZStandard() @staticmethod def registry_name() -> str: return "stream.zstd" def __init__(self) -> None: super().__init__() if not ZStandard.is_available(): raise ValueError( f"ZStandard extension is unavailable because no module named '{zstandard_module_name}' or '{pyzstd_module_name}'" ) def get_descriptor(self) -> str: return f"{self.registry_name()}/1" def transform_to(self, output: IO[bytes]) -> IO[bytes]: if zstandard is not None: compressor = zstandard.ZstdCompressor() # type: ignore[union-attr] return compressor.stream_writer(output) class Writer(io.RawIOBase): def __init__(self, output: IO[bytes]) -> None: self.output = output self.compressor = pyzstd.ZstdCompressor() # type: ignore[union-attr] def writeable(self) -> bool: return True def write(self, b: Buffer) -> Optional[int]: outdata = self.compressor.compress(b) if outdata: self.output.write(outdata) return len(memoryview(b)) def flush(self) -> None: outdata = self.compressor.flush() if outdata: self.output.write(outdata) self.output.flush() return cast(IO[bytes], Writer(output)) def transform_from(self, input: IO[bytes]) -> IO[bytes]: if zstandard is not None: decompressor = zstandard.ZstdDecompressor() # type: ignore[union-attr] return decompressor.stream_reader(input) class Reader(io.RawIOBase): def __init__(self, input: IO[bytes]) -> None: self.input = input self.decompressor = pyzstd.EndlessZstdDecompressor() # type: ignore[union-attr] def readable(self) -> bool: return True def readinto(self, b: Buffer) -> Optional[int]: # This needs to read enough so it can decompress # something so the output doesn't look like EOF. This # means reading at least one block. The max block # size is 128KB, so we read that plus some # overhead to be sure. if self.decompressor.needs_input: indata = self.input.read((128 + 6) * 1024) else: indata = b"" bview = memoryview(b) blen = len(bview) outdata = self.decompressor.decompress(indata, blen) if outdata is None: return None count = len(outdata) bview[:count] = outdata return count def seekable(self) -> bool: return False return cast(IO[bytes], Reader(input)) class ExtensionRegistry: def __init__(self) -> None: # Populate default registry contents self.extensions: dict[str, type[Extension]] = { cls.registry_name(): cls for cls in (ZStandard,) } def register(self, cls: type[Extension]) -> None: self.extensions[cls.registry_name()] = cls def from_descriptor_list(self, descriptors: Sequence[str]) -> Sequence[Extension]: """ Given a seuquence of descriptor strings as returned by Extension.get_descriptor at save time, creates a sequence of Extension instances. The name[@local-domain] preceding the version number is used to look up an implementation class in the registry, and the version is passed to the class's from_descriptor static method. If the registry contains no match, this will throw ValueError. If the from_descriptor method raises an exception, that will pass through to the caller. """ def from_descriptor(desc: str) -> Extension: name, _, version = desc.partition("/") if version is None: version = 0 ext = self.extensions.get(name) if not ext: raise ValueError(f"Unknown extension {name=}") return ext.from_descriptor(version) return [from_descriptor(desc) for desc in descriptors]